Channel 4's heavyweight documentary on two of the world's fattest people, Bodyshock: Half Ton Man, pulled in nearly 5 million viewers last night.

Telling the stories of 76-stone Patrick Deuel and 85-stone Rosalie Bradford, Half Ton Man drew an audience of 4.9 million viewers and a 19% share between 9pm and 10pm, according to unofficial overnights.

This was 700,000 more than tuned into Celebrity Big Brother in the same slot two weeks before.

The Channel 4 documentary, directed by Katinka Newman, revealed modern science's take on compulsive eating disorders and why some people literally eat themselves to death.

In Deuel's case, doctors had to remove a wall from the American's house in order to get him to hospital in a specially reinforced ambulance for a life-saving gastric bypass. But even after the operation he continued to snack, knowing that his compulsion could kill him.

Half Ton Man drew nearly double the 2.5 million audience for last week's Bodyshock, Curse of the Mermaid, which told the story of a Peruvian woman born with her legs fused together.

The show seemed to have eaten into the audience for ITV1's Robson Green drama Northern Lights, which was down by 500,000 viewers on last week's outing and BBC2's Balderdash & Piffle, down by an identical figure.

But BBC1's retro police drama Life on Mars added 300,000 viewers compared with last week in the 9pm to 10pm slot.

BBC1 homage to the 70s, starring John Simm, attracted 6.7 million viewers and a 26% share, against Balderdash & Piffle's 1.9 million and Channel Five's Medical Investigation with 900,000 viewers and a 4% share.

Northern Lights had to settle for 6 million viewers and a 23% audience share.

Bodyshock's appeal did not have a ripple effect on ER, which drew just 200,000 more viewers than last week, against Five's roller coaster jail drama Prison Break.

ER was watched by 2.3 million viewers and won a 13% audience share between 10pm and 11pm.

Five's gritty US series, Prison Break, staring up and coming actor Wentworth Miller, locked down 1.7 million viewers and a 9% share - down slightly on last week.

The last episode of the current series of The Thick of It, meanwhile, drew just 1.2 million viewers and a 6% share to BBC 2, 100,000 fewer viewers than Newsnight and four times fewer than the 5.1 million that tuned into BBC1's 10pm news.

Meanwhile, Channel 4's new series on women in their 30s choosing the DIY route to conception, The Baby Race, managed 900,000 and a 10% share at 11.05pm.